When comparing Scala vs Red, the Slant community recommends Scala for most people. In the question“What is the best programming language to learn first?”Scala is ranked 20th while Red is ranked 41st. The most important reason people chose Scala is:

Pros

Pro

Immutable values

The immutable values make it perfect for working with concurrency

Pro

Multiparadigm

Scala supports both Functional and Object Oriented styles of programming. Beginners can learn both paradigms without having to learn a new language, and experts can switch between the two according to what best suits their needs at the time.

Pro

Type inference

Scala offers type inference, which, while giving the same safety as Java's type system, allows programmers to focus on the code itself, rather than on updating type annotations.

Pro

Compiles to JVM bytecode

Aside from Java itself, Scala is by far the most popular of the many JVM languages. If you're developing for Android, or a similar JVM-only platform, or otherwise need out-of-the-box cross-platform compatibility, but the performance of a compiled language, Scala is the way to go.

Pro

Very good online courses

On coursera you can find great introduction to Scala by Martin Odersky.

Pro

Type inference leads to a simpler syntax

Pro

Pro

Simple toolchain

Other languages have complex, multi-step setups that beginners often get stuck on. Red has no installer, no setup, no dependencies*, just a single small (~1MB) command-line executable with both the compiler and repl. On Windows, you don't even have to launch executable from the command line--it has a GUI-console.

Pro

Very simple syntax

Red syntax is a lot like Rebol. It's easier than most languages for beginners to pick up.

Pro

Both low and high-level

Red has low enough access to do systems programming, but it's expressive enough for high-level scripting.

Pro

Low cognitive load

Red has very simple syntax that's easy to learn. It gets out of your way and lets you think about the problem instead, enhancing productivity.

Cons

Con

Can be intimidating for beginners

Scala is an industrial language. It brings functional programming to the JVM, but not with a "start small and grow the language" perspective, but rather a very powerful language for professional programmers.

Con

Static type system inherits cruft from Java

The type system is too complicated yet still less powerful than Haskell's.